An Israeli missile hits an area in Rafah, southern Gaza Strip, on July 9. / AP

by Miriam Hamed and Michele Chabin, Special for USA TODAY

by Miriam Hamed and Michele Chabin, Special for USA TODAY

GAZA CITY - Israeli warplanes pounded targets in Gaza on Wednesday as Israel moved to stop volleys of Palestinian rocket fire entering its territory and Prime Minister Benjamin Netanyahu vowed to return quiet to Israel's towns.

"Hamas will pay a heavy price for firing toward Israeli citizens," Netanyahu said. "The security of Israel's citizens comes first. The operation will expand and continue until the fire toward our towns stops and quiet returns."

Ashraf al-Qidra, a Palestinian health ministry spokesman, said at least 35 people have been killed since Israel's Operation Protective Edge aimed at quelling rocket fire against Israel began on Tuesday. More than 200 Palestinians have been wounded. Israel has not reported any deaths of its citizens since the offensive started.

Israeli airstrikes struck houses in the towns of Beit Hanoun and al-Fukhari, and the refugee camp of al-Bureij, as well as a building used by the military wing of Islamic Jihad Brigades - a smaller group than Hamas that opposes Israel's existence. Hamas controls Gaza.

Shadi Awad, 12, of Gaza City, lives next door to the headquarters of Hamas' police force. She said Wednesday that she was afraid.

"It (the police station) was bombed three times - each time, I hit the ground but then got up to watch out the window. There is just thick smoke and ambulances."

Bomb shelters in Gaza are scarce. Residents stayed home from work, students avoided school and many hurried to stockpile provisions even as supplies at stores ran low.

"The situation is becoming unbearable," said Om Mahmood, 58, of Khanyons in southern Gaza, who has seven sons and was attempting Wednesday to buy food for her family. "I was able to go to the nearest supermarket but found a lot of normal things gone, especially milk."

"When I heard we might go to war, I managed to buy flour for bread - it's enough for 15 days for my family," she said.

Israel has attacked more than 560 sites in Gaza. And militants from the Palestinian territory fired more than 225 rockets into southern and central Israel on Monday and Tuesday, according to the Israel Defense Forces.

On Tuesday night, militants expanded their attacks - which had been focused on southern Israel - to the center of the country. Residents of Jerusalem and Tel Aviv - Israel's two largest cities - were forced into bomb shelters at the sound of air raid sirens.

One rocket landed near Hadera in the center-north of Israel. Israel's Iron Dome anti-rocket system intercepted two rockets in the Tel Aviv region.

The escalation in hostilities has prompted fears that Israel could be preparing for a possible ground invasion of Gaza. Israel's Defense Minister Moshe Yaalon warned the offensive would be long term. "The price the organization will pay will be very high," he said.

Still, despite the onslaught of rockets, Israel is doing what it can to prevent a large-scale ground operation, says Barak Ben-Zur, a former IDF colonel and expert in strategic intelligence at the Inter-disciplinary Center in Herzliya.

The decision to rely on aerial strikes is based on cost and benefit, he says. "If there is an option to accomplish the mission by using precise intelligence and precise guided weapons, that's a better way to do it," he said.

Life for Israelis and Palestinians on both sides of the Israel-Palestinian border had been relatively quiet since the cease-fire that ended an eight-day military confrontation in November 2012.

However, the situation deteriorated last week after the bodies of three missing Israeli teenagers were found, followed a day later by the abduction of a Palestinian teenager in Jerusalem - who was later found burned to death in what Palestinians believe was a revenge attack. Six Jewish Israelis were arrested in the killing.

Raed Abusahlia, general director of Caritas Jerusalem, a Catholic humanitarian organization, urged both Palestinians and Israelis to consider the toll the violence is taking on their people.

"They have to stop the violence on both sides. They've experienced enough hardship, especially in Gaza. They have to stop. They have to stop. Enough!"

Odelia Ben-Porat, a mother of six who lives in Sderot, a small Israeli town near the Gaza border now under almost constant rocket fire, said she and her husband have had to scrap their summer plans - from summer camp for their kids to family outings.

Ben-Porat said she cannot allow her children to play outside because the time between a rocket's launch and landing is about 15 seconds, which is not enough time to reach shelter.

"We are in a constant state of danger," said Ben-Porat. You are always sitting on the edge of your chair wondering how long you have until the next Red Alert siren sounds."

Chabin reported from Jerusalem. You can follow her on Twitter: @michelechabin